Medium Format Stereo

by Oleg Vorobyoff

I recently bought an old Sputnik camera. I have since been carrying it with me everywhere. The big 50x50mm (2×2 inch) slides are such a pleasure to view, 35mm stereo seems toy-like in comparison. My new picture taking philosophy is, try to capture it on medium format first, then dig out the 35mm gear for a backup shot. This despite the unfortunate fact that medium format is virtually impossible to project. It needs to be viewed in a hand viewer.

Advantages of Medium Format

Unlike a 35mm stereo slide, a medium format slide is detailed and grain free. That is not to say 35mm is undetailed, but I always find it a relief to return to the crispness of real vision after a long session of slide viewing. I do not get that feeling after viewing medium format slides. Objects still look crisper in the real world than in the viewer, but only marginally so. I think you would need to go to a 4×5 inch format to approach 20/20 vision, but it is impossible to view such large stereo pairs without elaborate optical apparatus. I have looked through devices that use mirrors to view a pair large prints, but found that the viewers make the overall experience unsatisfying. A 6×6 stereo pair is about the largest that can be viewed with simple apparatus.

Medium format is well suited to the fine details of this autumnal scene by Oleg Vorobyoff. When the slide is examined in a medium-format viewer, multiple layers of sage, branch and leaf can be discerned.

The reduced magnification required by medium format yields all kinds of of additional benefits. The viewer lenses tend to introduce less distortion and optical aberration. Setting the stereo window and aligning the chips can be done with the naked eye instead of with advanced micro-surgical techniques. Dust is no longer an unrelenting enemy. In a pinch the stereo pair may be free-viewed through a simple pair of reading glasses. In fact, I sometimes find this more satisfying than conventional viewing. Less magnification makes the slide appear sharper and the stereo window more prominent.

One of the problems of 35mm stereo is that scenes in which you could swear you saw depth end up looking flat in the viewer. I often compensate by using a wider stereo base than normal, but at the risk of unnaturally miniaturizing the subject. For some reason I do not quite understand, medium format slides do not tend to rob a scene of depth. Stereoscopic vision seems to be very discriminating, demanding high resolution images to be fully exploited.

Another advantage of medium format, one that completely surprised me, is that you gain a good f/stop of contrast over 35mm using identical film. Somehow the greater surface area opens up the shadow areas of the slide. To take full advantage of this effect I find I need to underexpose medium format slides a half stop in most situations or a full stop under what I would give a slide intended for projection. This is truly liberating. Scenes containing both extensive areas of sunlight and of shadow are no longer to be avoided.

Formats

The conventional format uses 50x50mm apertures. This allows considerable cropping leeway over the 60×60 original slide – a bit too much in my opinion. I could live with 55×55 for mounting purposes, but this might be beyond the coverage of most viewers. After years of full frame 35mm photography I found the square format excruciatingly confining at first. You could have just as well lopped off both of my arms. But after a few weeks I learned to ignore peripheral subject matter and tunnel in on essentials. Realist photographers might ask what is so unsettling about a square format, but I think they too would have some difficulty with excessive sky and foreground in their first medium format shots. A 75mm medium format lens feels more like a 28mm lens than the 35mm on the Realist. Of course, there are landscape and portrait type apertures available in the standard mount if square is not your thing. I do feel that a landscape rectangular format is more natural. But that would be the subject of another essay.

Medium format also encompasses 6×7 and 6×9 formats. At one time I fantasized about shooting 6×9’s with extreme wide angle lenses to capture the full width of natural vision. But I quickly found that it is physically impossible to build viewer lenses with the necessary viewing angle. It is quite possible, however, to build a viewer for 6×7’s, as Kevin Chou so beautifully demonstrated. The trick is to view the chips a bit off the optical axis of the lenses. This puts the stereo pair at an apparent eye-spacing, just like a Holmes stereo card viewer. Kevin’s viewer has relatively low magnification, which allows the slide to be viewed comfortably in its entirety. I have also been experimenting with high magnification viewers for 6×7’s. Some 4x loupes work okay for this, but you need to shoot with proportionately reduced stereo base, since the added magnification stretches out the stereo space. My ultimate idea is to focus entirely on the meat of the stereo pair, eliminating all vestiges of a stereo window. I have yet to find lenses of sufficient magnification and viewing angle to bring this about, but have come close, so there is hope.

And what about 645? I have not heard this discussed, but could it be that the ideal format is a superslide with 40x40mm aperture? You could view it with most viewers designed for 35mm full frame – lots of which are available off-the-shelf. You could project it with a pair of Ektagraphics. And a 6×4.5cm original gives you lots of cropping options along the horizontal. Big problem might be to find a pair of reasonably priced 645 cameras. New cameras are priced out of sight – figure on at least $5,000 for a twin rig.

Shooting Medium Format

Your camera choices for medium format are much like for 35mm: dedicated stereo camera, twin rig or a shifted single camera. But every bit as important as the camera is the equipment with which you will ultimately view your slides. Your shooting technique must complement your viewer. See the following paragraphs for some tips.

The only easily available dedicated medium format stereo camera is the USSR-built Sputnik, now decades out of production. The Sputnik lenses do not compare with modern lenses, and would not yield satisfactory enlargements, but its stereo pairs are fine when viewed through standard 75 or 80mm lenses. I generally shoot at f/22 and preset my focus for that aperture. This means all I really need to set is my shutter speed; it’s almost point-and-shoot. Other than that, I just confirm that the near point is beyond 3 paces (7 feet) of camera position. Closer than that and you risk window violations. Despite its larger format, the Sputnik is lighter than my other stereo rigs. Unfortunately, the Sputniks are quirky and usually require some work before they will yield acceptable results. Try “Sputnik stereo camera” on Google to find web sites that describe what might be involved.

I have not used one, but can surmise that a medium format twin rig would be expensive, heavy, and difficult to match and synchronize. Furthermore, there are no medium format cameras I know of that are narrow enough to be mounted at eye spacing. But since a larger stereo base is often desirable this is not necessarily a show stopper. Like with the Sputnik, twin rig focus can be preset at a hyperfocal distance, but your near point will need to be set back, 10 feet away or farther, depending on stereo base. The 1/30 rule (near point at least 30 times the stereo base away) is a good rule of thumb to use with standard 75mm taking and viewing lenses.

Shifting a single camera gives you the ultimate in flexibility. You can set your stereo base at, say, 30mm to capture nearby objects or at many feet for distant hyperstereos. A tripod and slide bar are highly recommended. Again, the 1/30 rule is appropriate if distant objects appear in the picture. Otherwise, a wider stereo base is in order. Only caveat: nothing shall move between shots, not a blade of grass, not a shadow. Because of the added resolution, movement unnoticeable in 35mm can spoil a medium format shot.

The Achilles heel of medium format is shallow depth of focus. The added resolution makes lack of focus in any part of the picture all that more apparent. I would recommend shooting at a stop narrower than suggested by conventional depth of field tables. In fact, use a tripod and stop all the way down. Unlike with 35mm, I can detect no loss of sharpness at normal medium format viewing magnifications due to stopping down. Depth of focus can often be improved with view camera movements. Just don’t try to use the movements to “correct” the perspective lines. That only works for a flat print. The brain automatically makes all the perspective corrections needed for most situations, a tilted horizontal being the major exception.

Viewing Medium Format

If you want a fine viewer you need to build it yourself. Kits are available, or you can string together a pair of loupes. The only mass produced hand viewer I know of is the King Inn, which is acceptable but not much more. Conventional viewer lenses are 75mm in focal length. These provide a moderately wide, eye-filling view. Some photographers opt for wider lenses, say 65mm, for an even more immersive view. Then there are a few that go for 100mm. I’ll take one of each, thank you. As discussed previously, different viewers call for different stereo bases, and, for that matter, different compositional philosophies. Stereo base determines on-film deviation. With a 75mm viewer you want a maximum on-film deviation of about 2.5mm. That is, on a stereo pair having its nearest subject matter at the window, distant objects should have at most 2.5mm separation more than the separation of the mount’s apertures. For 65mm and 100mm viewers I would go for 2.0mm and 3.0mm maximums, respectively. However, since depth discrimination in medium format is so sensitive it is often possible to achieve effective stereo using just a fraction of the available maximum. As for composition, the view through 65mm lenses can be so wide that the window becomes practically irrelevant. The eye is drawn to the center of the slide and subject matter near the edges takes on secondary importance. Through 75mm lenses the entire slide is effectively center stage but the window is still relatively detached from the scene. Through 100mm lenses the window frame is in prominent view so it is easy to gage the relationship of the window to the subject matter. In short, the window behaves much like the frame of a conventional flat photograph.

Projecting Medium Format

In two words, forget it. Limitation on screen height means that a medium format slide will project no larger than a Realist slide in most rooms. Furthermore, the polarizing filters used in projection drain the image of much of the subtlety apparent through a hand viewer. Now if you could rent an Imax theater for an evening and find some way to adapt the projector for still pictures, you might have something worthwhile. But the sad fact is, there is no practical way for a large group to view medium format slides that does them justice.